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RE: Setting 9600 baud deviation?

> Van: Dale Coleman [mailto:kf4sir@earthlink.net]
> Hi all, I'm in the process of setting up my new TNC3S for 
> 9600 baud packet
> and was hoping to get some advise on setting the deviation.
> What I have done so far is use a second rig as a monitor and 
> hooked up my
> digital volt meter to the speaker jack measuring the voltage 
> as I increase
> the TNC output.  After finding a peak I backed down the TNC 
> output about
> 20% or so.
> The TNC3S is now working at 9600 baud but I can't help but 
> think it still
> needs some fine tuning.
> Anybody know of a better cheap way to fine tune the TNC?  It 
> seems to me
> the method above would work very well for 1200 baud but what 
> about audio
> clipping on the monitor radio at 9600 baud?
> Anybody know of a deviation meter available some place that is not too
> expensive?
> An oscilloscope can be used to check deviation right? 
> (Don't own one but it would have lots of other uses as well)
> I'm also curious if anybody has tried using a sound card 
> program with a
> water fall display like Digipan to take a look at the 
> received audio.  I
> think I will try this weekend - maybe it will help me find 
> any distortion
> that might be there.
> Thanks, Dale KF4SIR 

Here is the way I and most people around here do it:

hook up a second rx that you know has a good 9k6 out
transmit in the tx that you want to tune and feedback using the second rx to
the tnc.
hook up the scope to the rx eye test point on the modem and triger the scoop
using the rx clock.
now adjust the deviation and the fir filter until you get a nice open eye
with scharp crossovers at the top and bottem of the eye.

this is the best setting for any fsk g3ruh modulation.
there should be a picture in the manual (there was with the tnc2h)

Do not trust the speaker out for this as it has to many audio filters to
work good, get the signal direct from the discriminator.

73 de Andre PE1RDW
aprsdigi co-ordinator Netherlands
member aprs workgroup Netherlands

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